The death toll in Quebec's oil train disaster jumped to 13 people on Monday, July 8 and police said about 40 more people were missing, a sign the derailment and explosion could be the worst accident in Canada since the Swissair crash of 1998.

Police said they estimated a total of around 50 people were either dead or missing after the gigantic blast destroyed dozens of buildings in the center of Lac-Megantic early on Saturday.

Previously they had said the death toll was five and the number of missing was 40. Given the massive devastation in the town center after the blast, few residents expect any of the missing to be found alive.

If the death toll does hit 50, that would make it Canada's deadliest accident since 229 people died in 1998 when a Swissair jet crashed into the sea off eastern Canada.

The runaway oil tanker train derailed in Lac-Megantic shortly after one o'clock in the morning on Saturday (July 6), exploding in a deadly ball of flames.

Airbrakes that would have prevented the disaster failed because they were powered by an engine that was shut down by firefighters as they dealt with a fire shortly before the calamity occurred, the head of the railway that operated the train said on Monday.

The train had been parked at a siding on a slope near the town of Nantes, which is 12 km (8 miles) west of Lac-Megantic. The volunteer Nantes fire service was called out late on Friday night to deal with an engine fire on one of the train's locomotives.

Nantes Fire Chief Patrick Lambert told Reuters the crew had switched off the engine as they extinguished a "good-sized" blaze in the engine, probably caused by a fuel or oil line break in the engine.

The problem was that the engine had been left on by the train's engineer to maintain pressure in the air brakes, Ed Burkhardt, chairman of Montreal, Maine & Atlantic Railway (MMA), said in an interview. As the pressure gradually "leaked off", the air brakes failed and the train began to slide downhill, he said.

The fire service said it contacted a local MMA dispatcher in Farnham, Quebec, after the blaze was out

It was not immediately clear what the MMA dispatcher did after speaking with the fire service. Burkhardt said the fire service should have also tried to contact the train's operator, who was staying at a nearby hotel.

The center of Lac-Megantic, a lakeside town of 6,000 near the border with Maine, was still cordoned off on Monday morning. One of the destroyed buildings was a music bar popular with young people, and witnesses reported fleeing the area around the building as the heat and flames closed in.

Canadian crash investigators said they will look at the two sets of brakes on the train, the airbrakes and the handbrakes.

Montreal Maine & Atlantic is one of many North American railroads that have vastly stepped up shipments of crude oil as pipelines from North Dakota and from oil-producing regions in Western Canada fill to capacity, and the accident is bound to raise concern about the practice of transporting oil by rail.